Methods for growing ethylenediamine tartrate crystals



Patented Apr. 1, 1952 METHODS FOR GROWING ETHYLENE- DIAMINE TARTRATECRYSTALS Albert C. Walker, Short Hills, N. J., assignor to BellTelephone Laboratories, Incorporated, New York, N. Y., a corporation ofNew York No Drawing. Application August 11, 1950, Serial No. 178,983

7 Claims.

This invention relates to ethylenediamine tartrate crystals and moreparticularly to methods for growing the same.

One of the objects of this invention is to promote the growth rate ofthe crystals.

Another object of this invention is to provide crystals havingessentially no tapering of the prism faces.

Still another object of this invention is to produce a more perfectcrystal.

Yet another object of this invention is to stabilize the mother liquoragainst the appearance of spurious crystalline growth.

There are two common methods of growing ethylenediamine tartratecrystals, henceforth referred to as EDT crystals. These are: (1) bygradual reduction of temperature of a solution saturated at elevatedtemperature, and (2) by feeding a solution saturated at one temperatureinto a tank containing seed crystals kept at a constant temperatureslightly lower than the saturation temperature. Due to the formation ofthe hydrate at temperatures below about 40.6" C., excessivedecomposition of the heat sensitive EDT above about 50 C. and thetherefore consequent narrow permissible temperature range, the firstmethod has been replaced by the second in commercial production of thecrystals. By the above-mentioned methods up to this time, it has beendifficult to obtain an EDT crystal with parallel prism faces.

The saturated stoichiometric solution of EDT in water has a pH of about5.9. Crystallizing from such an acidic normal solution results in acrystal at which the prism faces show approximately a 16 per cent taper.Adding an excess'of ethylenediamine to bring the pH up to 7.2 has theeffect of reducing crystal taper to about 3 percent. However, adding anexcess of ethylenediamine has the unsatisfactory effect of reducinggrowth rate and of increasing spurious crystal growth, and furthermore,results in themcrease of polymerization of the EDT. Where this typesolution is used, it is necessary to stop production when aconcentration of polymerized polymer reaches about 8 per cent. Theproblem then has been to reduce the taper of the EDT advantageouslyimproves crystal production in that by its use it is possible to grow acrystal with substantially no tapering of the prism faces while at thesame time approximately doubling the growth rate and impeding thespurious crystal growth. Also, this process impedes formation of thepolymerized EDT and allows the concentrationof the polymerized EDT torise to from 10 to 14 per cent before it becomes necessary to stop theprocess and clean the tanks, whereas, by methods before in use, theallowable concentration of the polymer was 8 per cent.

In the present invention the EDT crystals are grown from seeds in asaturated EDT mother liquor which liquor pH is maintained at any desiredvalue with the addition of ammonium hydroxide. It has been foundadvisable to limit the pH range to from 6.5 to 8 since below 6.5 theresultant crystal is so severely tapered as to be commerciallyimpracticable, and since at above 8, the formation of the polymer is aserious problem. Comparative data have been kept on crystal growth froma solution containing ammonium hydroxide in amounts necessary tomaintain the pH at about 7.5 as compared with growth from a solutioncontaining an excess of ethylenediamine in amounts necessary to maintaina pH of about 7.2. Sets of data were kept on constant temperature anddropping temperature runs. It was found that Whereas the crystalproduced from a, solution containing an excess of ethylenediamine hadprism faces which showed about a 3 per cent taper, crystals grown fromthe solution containing ammonium hydroxide showed essentially no taper.Whereas the growth rate in a solution containing an excess ofethylenediamine was only about 0.0294 inch per day, growth rates of upto 0.60 inch per day were achieved in a solution containing ammoniumhydroxide.-- Furthermore, it was found practicable to allow the polymerconcentration to rise to from 10 to 14 per cent in the solutioncontaining ammonium hydroxide, whereas in the solution containing anexcess of ethylenediamine, but no ammonium hydroxide, the growth processhad come to a substantial halt when the polymer concentration reached 8per cent.

A detailed description of a dropping temperature process utilizing thepresent invention follows:

EDT seeds grown by known methods are mounted on a spider and placed in atank. A saturated solution of EDT in water is made up at about C. and iskept at that temperature. To this solution sufficient ammoniumhydroxideis added to bring the pH to about 7.5. alkaline solution isnext poured into the tank which latter has been preheated to 60 C. sothat the The main disadvantage in the dropping temperature method ofgrowing EDT crystals is the high decomposition rate above 50 C. and theconsequent, slow growth rate.

The preferred process utilizing this invention is by growth of thecrystals from. a supersaturated solution kept at constant temperature. Adetailed description of one such process follows:

, EDT seeds grown by" known methods are mounted. on a spider and placedin a tank. A saturated solution of EDT in water is madeup at about 43 C.Such a saturated solution contains about 63 weight per cent of EDT. Tothis solution sufiicient ammonium hydroxide is added, to bring the pH'toabout 7.5. This alkaline solution is next run into a superheating tankin which the temperature is kept at about 46 or 47 C. The solution thenpasses into a crystallizing tank which tank, including a spider andcrystals, has been preheated for several hours preceding (12 hours hasbeen found to be ample) at a temperature of about 54 C. The wholecrystallizer tankand contents is then kept at a temperature of about. 42C. so as to result in a supersaturation of about 1 C. Excess EDT isadded at regular intervals tothe saturating tank which EDT passesthrough the superheating tank and then into the crystallizer. Thetemperature of the crystallizing tank is kept at the growingtemperature, which as above noted, is in the neighborhood of 42 C. Thisprocess is allowed to corn tinue. for periods of about three months, itbeing necessary to stop and drain the solution at any time that polymerconcentration rises to from to 14 per cent.

A more detailed description of this constant temperature process and ofone type of equipment which has proved to be very satisfactory, may befound in United States Patent No. 2,459,869.

Examples have been given of the application of this invention to onedropping temperature process and one constant temperature process. Theinvention is obviously applicable to any process for the growing of EDTcrystals where it.is desirable to reduce taper, to increase growth rateand to receive the other benefits. outlined above. It is intended toinclude all methods of growing EDT crystals in the presence of ammoniumhydroxide.

. What is claimed is:

'1. A process comprising growing ethylenediamine tartrate crystals fromseeds in a mother liquor supersaturated with ethylenediamine tar- 4trate, which solution is maintained alkaline at a pH of from 6.5 to 8 bythe presence of ammonium hydroxide and at a temperature of from about406 C. to 50 C.

2. A process comprising growing ethylenediamine tartrate crystals fromseeds in a mother liquor supersaturated with ethylenediamine tartrate,which solution is maintained alkaline at a; pH of about 7.5 by thepresence of ammonium hydroxide and at a temperature of from about 40.6"C. to 50 C.

3. A process comprising growing ethylenediamine tartrate crystals fromseeds in a solution saturated-.with ethylenediamine tartrate at elevatedtemperatures by gradually reducing the temperature of the solution fromabout 50 C.

" to about 406 C. so as to keep it supersaturated at all times, whichsolution is maintained at a pH of from 6.5 to 8 by the presence ofammonium hydroxide.

4. A process comprising growing ethylenediamine tartrate crystals fromseeds in a solution saturated with ethylenediamine tartrate at elevatedtemperatures by gradually reducing the temperature of the solution fromabout 50 C. to about 40.6" C. so as to keep it supersaturated at alltimes, which solution is maintained at: a pH of about 7.5 by thepresence of ammonium hydroxide.

5. A process comprising growing ethylenediamine tartrate crystals byfeeding a solution saturated with ethylenediamine tartrate at onetemperature into a tank containing seed crystals kept at a constanttemperature in the range of from 40.6 C. to 50 C. which temperature isslightly lower than the saturation temperature and in which the solutionis maintained atapH of'from 6.5 to 8 by thepresence of. ammoniumhydroxide. I

v 6. A process comprising growing ethylenediamine tartrate crystals byfeeding a solution saturated with ethylenediamine tartrate at onetemperature into a tank containing seed crystals kept at a constanttemperaure in the range of from 406 C. to 50 C. which temperatureis',slightly lower than the saturation temperature and in which the solutionis maintained at a pH of about 7.5 by the presence of ammoniumhydroxide.

7. A process comprising growing ethylenediamine tartrate crystals bywhich a saturated ethylenediamine tartrate solution is madeup at atemperature of about 43 C., superheated to 46 or 47 C., and then passedintov a crystallizer whichv crystallizer together with its contentsisthen kept at a constant temperature of. about 42 C.,and in which the pHis maintained alka linev at about 7.5 by the addition of ammoniumhydroxide, and, in which the solution in the crystallizer is keptsupersaturated by the'addition of ethylenediamine tartratesolutionsaturated at about 43 C. at regular intervals.

ALBERT C. WALKER...

No references cited.

1. A PROCESS COMPRISING GROWING ETHYLENDIAMINE TARTRATE CRYSTALS FROMSEEDS IN A MOTHER LIQUOR SUPERSATURATED WITH ETHYLENEDIAMINE TARTRATE,WHICH SOLUTION IS MAINTAINED ALKALINE AT A PH OF FROM 5.5 TO 8 BY THEPRESENCE OF AMMONIUM HYDROXIDE AND AT A TEMPERATURE OF FROM ABOUT 40.6*C. TO 50* C.